Watch videos in high quality automatically. Now has a UserScript command to toggle a confirmation box. Made for people who don't login or save cookies. Uses JavaScript instead of &fmt=18; no reloading pages

Adds &fmt=18 to the url for high quality but not if &fmt=6 or &fmt=18 already exist

Simply adds a link to the fmt=18 version of a video. (Screenshot included)

Optimizes YouTube for bigger resolutions and gives you the opportunity to hide various sections of the video playback page, disable autoplay, enable HD and download videos. All this and more can be utilized through a built-in configuration menu: